A biped walking robot as it is called in the art comprises a main body having at both sides of its lower part a pair of leg portions attached thereto so as to be each pivotally movable biaxially, each of the leg portions having a knee portion in its midway and a foot portion at its lower end, the foot portions being attached to their corresponding leg portions so as to be pivotally movable biaxially, joint portions supporting the leg, knee, and foot portions for pivotally moving them, respectively, a drive means for pivotally moving the joint portions, a gait former for forming gait data in accordance with a targeted motion, and a walk controller for drive-controlling the drive means based on the gait data.
In accordance with the thus constituted biped walking robot, a pre-determined walk pattern (hereinafter referred to as “gait”) data is formed by a gait forming part, drive means is drive-controlled by the walk controller in accordance with the gait data, and thus the biped walking is realized by pivotally moving respective joint portions of the leg, knee, and foot portions in accordance with the pre-determined walk patterns. Here, in order to stabilize walk postures, a stabilization of a robot is targeted by ZMP (Zero Moment Point) regulation by what is called ZMP Compensation, whereby the points on the sole of a foot of the robot at each of which the composite momentum of floor reactive force and gravity becomes zero are converged to a target value.
Incidentally, the respective joint portions of such biped walking robots comprise active drive joints to be driven by drive means, or passive joints to be freely moved by being liberated from drive means.
The drive joints, which actively drive respective actuators as the drive means to pivotally moving joint portions, are to realize a walk by moving the leg and foot portions. The drive joints show such a merit as to form gait relatively freely by actively driving joint portion actuators. However, the drive joints had also the problem such as to increase energy consumption in general, and to make more complex control regulation with more joint portions in number, since they positively utilize the torque of actuators. Also, there was such a problem that a free gait formation is remarkably restricted by the ZMP criterion.
On the other hand, the passive joints are such as to pivotally move passively joint portions by such external force as gravity etc without using actuators. Since the passive joints pivotally move joint portions only by external force upon biped walking, the natural stability is realized, and ZMP is converged to soles. Further, since the passive joints save consumption energy as well as simplify control regulation, it is possible to lower a computation cost for walk control. However, since the passive joints are pivotally moved depending on external force such as gravity etc, it is difficult to realize a free pivotal movement, and a free walk.
Although the drive joints and passive joints have thus mutually opposing merits, the researches about them are conducted independently from each other, and most of the conventional biped walking robots use only the drive joints. Consequently, with the biped walking robot provided only with drive joints, a consumption energy of actuators to the drive joint portions is increased. On the other hand, the walking robots provided only with passive joints have long been known as toys, but they can not walk freely, and do not have sufficient walk stability.
Although the development is also carried out of the biped walk control combining the merits of both drive and passive joints, it is simple combination of drive and passive joints, with the joint portions as drive joints always act as drive joints, whereas the joint portions as passive joints always act as passive joints, and they are not really practical.